1. Field of the Invention
The present invention relates generally to a method for determining rotational data from a random pulse pair generated by an encoder device and, more particularly, to a method for determining rotational data that minimizes the effect of a cyclical anomaly that is associated with the output of an encoder device.
2. Discussion
Encoder devices are commonly used to monitor the rotation of instrumented vehicle wheels and other rotating devices. Physical inaccuracies inherent in any real system give rise to an anomaly or scattering in the actual measurement process, which we will refer to as "jitter" in the measured data. Since this jitter is repetitive in nature, it can be cancelled with an appropriate algorithm.
Traditional approaches for deriving angular position or linear displacement in the case of a wheel has been to sum received pulses from the encoder device. This approach is not affected by the jitter contained in the signal, and thus the present invention does not address distance measurements.
There are at least two methods commonly used for determining speed from an encoder signal. The first and most common method is to sum pulses over a fixed period of time (i.e., the frequency method). The calculation for this method is speed=(sum of pulses/time interval)*(rotational distance). In order to get acceptable resolution for the velocity calculation, the time interval must be large enough to see many pulses which in turn has the effect of limiting update rates. The second method uses the time interval between successive pulses to determine an instantaneous speed (i.e., the period method). The period method can give an updated speed value as each pulse arrives from the encoder, but it exhibits jitter in the measured data.
Therefore, it is desirable to provide a method for determining rotational data from a random pulse pair generated by an encoder device that minimizes the effect of the cyclical anomaly or jitter that is associated with the output of an encoder device.